Print hammer assembly method

Abstract

The impact pins of a matrix printhead are brazed by a laser to a print hammer of the flat spring type. The print hammers are then attached to a printhead mounting block adjacent to each other with the impact pins in substantially a straight line. The attached print hammers are then shaped by an electric discharge machining (EDM) process by a single electrode to simultaneously machine the impact pins to the desired shape and to position the tips of the impact pins at a precise distance with respect to one another.

We claim: 
     
       1. A method of manufacturing a matrix printhead comprising the steps of: providing a plurality of spaced apart elongated flat spring hammer elements;   securing an impact pin to each hammer element, wherein each impact pin has a tip which defines a dot to be printed and a tip configuration which is different from that desired for the printhead;   attaching the hammer elements to a printhead assembly; and   subsequently shaping the impact pins so that they have the desired tip configuration and so that they are accurately spaced with respect to each other.   
     
     
       2. The method of claim 1 wherein the impact pins are simultaneously shaped by means of an electric discharge machining process. 
     
     
       3. The method of claim 1 wherein the step of securing is accomplished by brazing the impact pin to the hammer element. 
     
     
       4. The method of claim 3 wherein the brazing includes the steps of directing a laser beam toward the spring in the area of the pin to heat the spring and subsequently positioning a brazing material adjacent the impact pin to melt the brazing material. 
     
     
       5. The method of claim 4 wherein the brazing material reflects the laser beam, whereby when the brazing material melts and flows into the area surrounding the impact tip it will reflect the laser beam to thereby avoid further heating of the spring. 
     
     
       6. The method of claim 1 wherein the step of shaping includes the step of tapering the impact pin adjacent the impact tip to thereby avoid sharp edges at the impact tip. 
     
     
       7. The method of claim 1 wherein the impact pin is carbide and wherein the step of shaping is accomplished by an electric discharge machining process. 
     
     
       8. The method of claim 7 wherein the electric discharge machining process employs an electrode including a flat surface having a plurality of recesses formed therein which correspond to the desired configuration of the impact tips, wherein the machining process includes the steps of positioning the electrode a predetermined distance from a reference mounting surface of the printhead assembly and generating high voltage sparks between the electrode and the impact pins. 
     
     
       9. The method of claim 7 wherein the recesses have a generally conical configuration. 
     
     
       10. The method of claim 8 including the steps of providing a punch having a configuration corresponding to the desired configuration of the impact tips and punching the electrode with the punch to form the recesses. 
     
     
       11. The method of claim 8 wherein the electrode is formed by forming grooves in the surface of a pair of pieces of electrode material and securing the pieces together so that the grooves together define the recesses. 
     
     
       12. A method of manufacturing a print hammer assembly comprising the steps of: providing a plurality of hammer body portions, each body portion having a hole formed therein;   inserting an elongated impact pin into each hole, wherein the impact pins have an impact tip having a cross-sectional configuration different from that desired for the print hammers of the assembly;   bonding each impact pin to its respective body portion;   securing the body portions to a hammer mounting assembly; and   subsequently shaping the impact pins to provide the desired impact tip configuration and to provide the desired spacing between the impact tips.   
     
     
       13. The method of claim 12 wherein the step of bonding is accomplished by brazing the impact pins to the body portions. 
     
     
       14. The method of claim 13 wherein the step of shaping is accomplished by an electric discharge machining process in which the face of an electrode having a plurality of recesses formed therein is positioned a predetermined distance from a reference surface of the hammer mounting assembly with a recess located in facing relation to each impact pin, wherein machining is accomplished by generating electric discharges between the electrode and impact pins, wherein the recesses are spaced from each other by an amount necessary to achieve the desired spacing between impact tips. 
     
     
       15. The method of claim 14 wherein the recesses are generally conical in shape. 
     
     
       16. A method of manufacturing a printhead assembly comprising the steps of: providing a plurality of hammer body portions, each body portion having a hole formed therein near a free end thereof;   inserting an elongated impact pin having an impact face into the hole in each body portion;   bonding each impact pin to its respective body portion;   attaching the body portions to a hammer mounting assembly adjacent to one another so that the impact pins lie substantially along a single line; and   subsequently subjecting the impact pins to an electric discharge machining process to shape the pins into a predetermined configuration to thereby provide a hammer assembly in which the impact faces of the pins have the desired configuration and are precisely positioned with respect to each other.   
     
     
       17. The method of claim 16 wherein the machining process employs a single electrode having a plurality of recesses formed therein, wherein the configuration of each recess corresponds to the desired configuration of the impact tips and wherein the recesses are separated by an amount necessary to precisely achieve the desired spacing between impact tips. 
     
     
       18. A method of manufacturing a matrix printhead comprising the steps of: providing a plurality of flat springs which are connected to a common member to form a comb-like structure;   securing an impact pin to each spring, wherein the tips of the pins define dots to be printed and have a configuration different from the desired impacting surface for the hammers;   subsequently shaping the impact pins to form impact tips having the desired configuration and spacing with respect to each other; and   securing the comb-like structure to a printhead assembly.